The present invention relates to an automatic transmission system for vehicles employing a gear-type transmission, in which the gear change operation of the gear-type transmission is automatically carried out with reference to a predetermined gear change map in accordance with the operating condition of the vehicle at each instant.
In the prior art, there have been proposed various automatic transmission systems for vehicles comprising a gear-type transmission with an actuator for changing gears in response to electric signals, and a gear change map for determining the appropriate gear position on the basis of the amount of operation of an accelerator pedal and the vehicle speed, whereby the gear-type transmission is automatically shifted in accordance with the result of the calculation based on the gear change map (for example, see Japanese Patent Publication No. 126141/84).
In the gear change map calculation of the prior art, the optimum gear position of the gear-type transmission is determined in accordance with only the amount of operation of the accelerator pedal and the vehicle speed. Therefore, whenever the vehicle speed increases, even, for example, at the time of hill climbing, the gear-type transmission is shifted up in accordance with the gear change map. Under certain circumstances, therefore, the vehicle speed is likely to decrease during disengagement state of the clutch required for shifting the gear-type transmission, whereby a change in the target gear position sometimes occurs. Consequently, during or just after the operation for changing gears, the gear is changed into a position other than the initial target position. This results in frequent meaningless gear shift operations, making it difficult or impossible to obtain sufficient acceleration of the vehicle and impairing the smoothness of vehicle operation.